Development of spill feedback control method for proton synchrotron

A Spill feedback method for proton synchrotron for cancer therapy has been developed and evaluated by computer simulation of the slow extraction with third order resonance. In our beam extraction scheme, the separatrix is shrunk by sweeping the RF cavity frequency to increase the momentum of the beam, which causes the beam to be swept to the outside across the separatrix. This means that the spill intensity depends on the rate of change of the separatrix area and the Courant-Snyder invariant distribution inside the separatrix. From this point of view, the rate of change of the RF cavity frequency was selected as the variable in our spill feedback system to control the spill structure. The simulation results show that our proposed feedback method is effective for controlling the spill intensity and for suppressing the fluctuations due to ripples in the bending magnet current. (author)